This invention relates to turbine types of power plants and particularly to means for improving fuel consumption.
As is well known the lowest possible fuel consumption of a gas turbine power plant is realized when the engine is operating at very high pressure ratios. It is also well known that owing to such high pressure ratios when the aircraft operates at low altitudes certain problems are manifested that are deleterious to the engine parts and performance. Namely, the high pressure heavier components to maintain structural integrity, engine hardware becomes expensive since exotic materials from which they are fabricated are necessary to withstand the high temperatures and performance is impaired because of the aggravation associated with thermal growth and the need for additional cooling air for the burner and turbine hot parts.
I have found that I can obviate these problems and obtain an efficacious power plant that affords maximum fuel economy by designing the engine with a very high compression ratio and operating the high spool at substantially full speed and at substantially full pressure ratio at low altitude. To this end, this invention contemplates maintaining the exit temperature of a multiple spool axial flow compressor at or near the altitude cruise or climb value by incorporating bypass means ahead of the high spool for controlling the pressure of the air supplied to the high spool. As will be appreciated by those skilled in this art since the compressor exit temperature must be held constant over the entire operating range, this invention contemplates incorporating certain variable engine geometry features which may be necessary to optimize this control mode. Some of these features may include one or more by the following:
1. variable pitch propeller PA1 2. variable pitch fan PA1 3. variable fan stators PA1 4. variable fan exit duct nozzle PA1 5. variable stators in the low pressure compressor PA1 6. variable pitch blades in the low pressure compressor PA1 7. variable area nozzles in the low pressure turbine and PA1 8. variable primary jet nozzle area
Obviously, the choice of these features for obtaining the best engine configuration will depend on the specific aircraft application and mission.